There continues to be strong interest in the development of high temperature superconducting wires and tapes for applications such as magnets, transmission lines and magnetic energy storage systems. The superconducting material most usually employed for these tapes and wires is a 2-2-2-3 phase of lead-doped bismuth-strontium-calcium-copper oxide wherein the numbers represent the approximate respective molar ratios of the bismuth, strontium, calcium and copper substituents. In a typical wire preparation, a partially sintered powder, i.e., a powder consisting primarily of a combination of 2-2-1-2 phase bismuth-strontium-calcium copper oxide and other calcium, copper and lead-containing phases that will yield the desired 2-2-2-3 phase upon subsequent sintering, is loaded into a tube, e.g., a silver (Ag) tube, and then mechanically deformed into a thin wire and/or tape. After deformation, the final conversion via sintering to the 2-2-2-3 phase takes place.
U.S. Pat. No. 5,300,486 discloses and teaches various processes for the preparation of superconductors such as the lead-doped bismuth-strontium-calcium-copper oxide superconductor including preparation from the respective metal carbonates, metal oxides or metal nitrates. While such processes are known, these processes typically involve long sintering stages of about 300 hours or longer. Thus, there remains a need for further simple, economical processes that will enable the preparation of the 2-2-2-3 lead-doped bismuth-strontium-calcium-copper oxide product. U.S. Pat. No. 5,300,486 uses a relatively inert material Sr.sub.9 Ca.sub.5 Cu.sub.24 O.sub.41 as a principal component, along with Bi-4334 and Ca.sub.2-x Sr.sub.x PbO.sub.4, where x has a value between 0-2. This mixture is slow to react and requires long annealing times (&gt;300 hours) to form the Bi-2223 phase in wires while this invention uses the highly reactive material Ca.sub.0.45 Cu.sub.0.55 O.sub.2 as a precursor phase. This phase decomposes rapidly in the presence of the other precursor phases (Bi-2212, Ca.sub.2 PbO.sub.4, and CuO) in the silver matrix. The resulting chemical reaction forms the superconducting Ag-clad Bi-2223 wire, in a much shorter time (&lt;200 hours).
Applicants show that (Bi,Pb)-2223/Ag-clad wires can be synthesized with average critical current of 20,000 A/cm.sup.2 using a two-powder mixture of the Bi.sub.1.8 Pb.sub.0.4 Sr.sub.2 CaCu.sub.2 O.sub.8 phase combined with a Ca.sub.0.45 Cu.sub.0.55 O.sub.2 and CaO powder. In addition, applicants have prepared the Bi.sub.1.8 Pb.sub.0.4 Sr.sub.2 CaCu.sub.2 O.sub.8 powder with a relatively high Pb content and less Ca.sub.2 PbO.sub.4. Annealing time is about 192 hours or 1/3 less than that of the process of U.S. Pat. No. 5,300,486.
Accordingly, it is an object of the present invention to provide a method of synthesizing a BiSrPbCaCuO superconductor material.
Still another object of the invention is to provide a first precursor mixture of calcium copper oxide, and calcium oxide and a second precursor mixture of BiSr.sub.2 CaCu.sub.2 O.sub.x =8.9, and Ca.sub.2 PbO.sub.4.